The boat sailed 12 km against the current and 18 km along the river, spending 2 hours for the entire journey.

The boat sailed 12 km against the current and 18 km along the river, spending 2 hours for the entire journey. Find the boat’s own speed if the river speed is 3 km / h

Let the boat speed be x
against 12 x-3
18 x + 3
12 / (x-3) + 18 / (x + 3) = 2
12x + 36 + 18x-54-2 (x ^ 2-9) = 0
30x-18-2x ^ 2 + 18 = 0
2x ^ 2-30x = 0
2x (x-15) = 0
x = 0 or x = 15
Answer: 15